noun, noun which may take the genitive case particle 'no'
unidentified; name unknown
Used in formal or official contexts to indicate that a person's name cannot be determined. Often appears in police reports, news articles, or administrative documents.
事故の被害者は姓名不詳のまま病院に運ばれた。
The accident victim was taken to the hospital with his name unknown.
警察は姓名不詳の遺体の身元を調べている。
The police are investigating the identity of the unidentified body.
身元不明 also means 'unidentified', but focuses on the person's identity as a whole, while 姓名不詳 specifically means the name is unknown.
Compound of 姓名 (name) and 不詳 (unknown, not detailed). The exact historical derivation is uncertain, but the word follows standard Sino-Japanese word formation patterns.